Gamma not changing

Hi there,
I’m trying to adjust the gamma on my monitor to linearize it, but changing the gamma values in the monitor centre seems to make no difference; what am I missing?

This issue was initially on Psychopyv2023.2.2 on a Windows 10 pc (version 22H2), but I have since updated to windows 11 and PsychoPyv2023.2.3.

The monitor is a Dell OLED (AW3423DW) running with 10bits per colour. This is the only monitor, and it is in landscape.

I am measuring luminance with a spyderX pro, which I run with DisplayCal on a separate machine.

I have measured the luminance at a range of values and seen the values are not linear, and run the psychopy monitors.GammaCalculator to get a suggested gamma value but this seems to make no difference. If fact, I get the same luminance measurements when the gamma is set to 0.8, 2.3 or 3.0. The attached figure shows measurements after I set the gamma in the monitor centre, saved the Monitor and restarted psychopy. There are three lines there, but they are on top of each other as values are practically identical.

I don’t think this is due to the error mention on the website due the the Windows 1903 version, as this is the only monitor and it is landscape.

Any suggestions for why this might be?